In U.S. Pat. No. 4,030,424 assigned to the same assignee as the present application, a railway car truck is disclosed having a pair of transversely spaced side frames joined by a transverse plate rigidly connected to the lower portion of each side frame to maintain the truck in tram. A bolster including a center bearing extends between the side frames and rests upon spring groups located in vertical slots in the side frames. The weight of the car body is taken on the bolster above the spring groups.
However, the tendency for the side frames to rock respectively in vertical planes about a transverse axis is believed to result in high stresses at the side frame--transverse member joint which may cause fatigue cracks to form.
In U.S. Pat. Nos. 2,976,819; 3,313,245 and 3,817,188, a pair of longitudinally spaced transoms extend transversely between the side frames to maintain the truck in tram. Diagonally spaced cylindrical connections are provided between the transverse members and the side frames. In U.S. Pat. Nos. 2,976,819 and 3,817,188, a resilient sleeve is provided between a rigid collar mounted on the side frame and a cylindrical extension of the transverse member.
However, the requirement of two transverse members to maintain the truck in tram makes these trucks expensive. SUMMARY OF THE INVENTION
In a railway car truck a transom bearing assembly is provided including a pair of tubes rigidly connected to each side frame. The tubes are longitudinally and vertically aligned. Near the center of the truck, generally below the center plate, a bearing member is rigidly connected to one of the tubes. The bearing extends within a portion of the adjacent tube. Low friction material located on the outer surface of the bearing and/or the internal surface of the surrounding tube allows relative rotation between the bearing and the surrounding tube as the side frames rock in vertical planes about a transverse axis as ups and downs in the track are traversed. Preferably a collar is rigidly connected to one of the transverse members to define the surrounding surface for the bearing. Also preferably the low friction material is a polymeric material having long wear, most preferably nylon-based, and a relatively constant coefficient of friction with the adjacent metallic surface to obtain a satisfactory, long-life bearing assembly. However, the transom resists the tendency for the side frames to move longitudinally with respect to each other, and thus maintains the truck in tram.